Along with the recent development of advanced information society, there has been a growing need for flat-panel displays. Known examples of flat-panel displays include non-self-light-emitting liquid crystal displays (LCDs), self-light-emitting plasma displays (PDP), inorganic electroluminescent (inorganic EL) displays, and organic electroluminescent (hereinafter referred to as “organic EL” or “organic LED”) displays, etc. Among these flat-panel displays, organic electroluminescent displays have made notable progress.
Improvements in materials and multilayering of device structures have so far been made for improving the luminous efficiency and life of organic EL displays. In particular, a multilayer structure shown in FIG. 5 is presently available for the realization of high-efficiency and long-life organic EL elements with use of phosphorescent materials. This multilayer structure includes an anode 32, a cathode 39, and six layers sandwiched between the anode 32 and the cathode 39. The six layers are a hole injection layer 33, a hole transport layer 34, a light-emitting layer 35, a hole blocking layer 36, an electron transport layer 37, and an electron injection layer 38. FIG. 5 is a schematic view showing a configuration of a conventional organic electroluminescent element.
Meanwhile, Non-patent Literature 1 discloses an organic EL element having a simple structure called “homo junction” made with a bipolar material that exhibits high charge mobility. FIG. 6 is a schematic view showing a configuration of a conventional organic electroluminescent element.
As shown in FIG. 6, an organic EL element 40 of Non-patent Literature 1 has such a simple structure that a positive and negative charge transporting light-emitting layer 47 containing a positive and negative charge transporting material is sandwiched between an anode 42 provided on a substrate 41 and a cathode 43. The positive and negative charge transporting light-emitting layer 47 includes an acceptor-doped region 44 doped with an acceptor, a light-emitting-material-doped region 45 doped with a light-emitting material, and a donor-doped region 46 doped with a donor. Non-patent Literature 1 discloses emitting EL light with both fluorescence and phosphorescence and emitting three primary colors of EL light, namely blue, green, and red EL light, in such a simple-structured organic EL element.